JPH08202110A - Image forming device - Google Patents

Abstract

PURPOSE: To prevent the occurrence of reduction in the density of a toner image, a color mixture, etc., even if a toner image developed on an electrostatic latent image exists by applying a DC voltage on which AC voltages having a different frequency and amplitude are superimposed, as a developing bias voltage. CONSTITUTION: The toner image of the second color is formed on a photoreceptor drum 1 on which the toner image of the first color is formed and an image exposure corresponding to the image of the second color is attained by a first latent image forming means 3b, to form the second electrostatic latent image. This development is attained in such a manner that black toner is stuck to the second electrostatic latent image by a developing electric field formed by the developing bias voltage which is applied from a developing bias supply 10b and composed of the DC voltage on which two kinds of AC voltages having the different frequency and amplitude are superimposed. The two-color image is transferred to a recording sheet 11 by the electrification of a transfer corotron 6 and the recording sheet 11 is peeled from the surface of the drum 1 by the electrification of a peeling corotron 7 and then, fixed to form the two-color image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer or a facsimile which uses an electrophotographic recording system or an electrostatic recording system, and in particular, has been improved to realize good development. Image forming apparatus.

[0002]

2. Description of the Related Art In recent years, in image forming apparatuses such as copying machines, printers, and facsimiles, there is an increasing demand for multicolor and full color. For example, as a color image recording apparatus using an electrophotographic recording system, various developing systems are known, and one of them is a so-called overlapping developing system. In this overdeveloping method, a toner image of each color component is sequentially developed on a latent electrostatic image bearing member such as a photoconductor to develop a color toner image, and then the color toner is collectively printed on a recording sheet. A color image is formed by transfer. The color image recording apparatus adopting such an overdeveloping method requires only one electrostatic latent image carrier, and does not require a transfer drum or the like for holding the recording sheet and conveying the sheet in pressure contact with the electrostatic latent image carrier. Therefore, the size of the electrostatic latent image carrier can be reduced, and the electrostatic latent image carrier can be reduced in size by arranging a charging device, an exposing unit, a developing device, etc. adjacent to each other for each color component around the electrostatic latent image carrier. Since a plurality of toner images can be formed during rotation, it has an advantage that the image forming speed is extremely high.

However, in the color image recording apparatus adopting this overdeveloping method, the second image following the development of the first color is used.
In the developing process after the color, the toner image already developed on the electrostatic latent image carrier is remarkably disturbed because it passes through the developing area facing the developing device again, and as a result, the color image finally obtained is There is a drawback that the image quality is significantly deteriorated. Further, the toner image formed in the developing process for the first color is scraped off from the electrostatic latent image carrier by the magnetic brush of the developing device in the developing process for the second color and thereafter, However, there is a problem in that the toner image density of the first color is reduced, and the life of the developer accommodated in each developing device for the second and subsequent colors is significantly reduced.

Conventionally, as a color image recording apparatus that solves the problems related to the developing process for the second and subsequent colors in the overdeveloping method, an electrophotographic recording apparatus employing a non-contact developing method has been proposed. Yes (Tokuhei 2-490
3 gazette).

That is, in the electrophotographic recording apparatus disclosed in the above publication, the first latent image forming means and the first developing means are arranged around the photoconductive drum-shaped recording body, and the downstream side thereof. A second latent image forming means and a second developing means are provided,
As the second developing means, a DC bias voltage having the same polarity as that of the charge latent image is applied between the drum-shaped recording medium and the sleeve-shaped developer conveying rotary member having a fixed magnet roll installed therein and the sleeve. An alternating bias voltage is applied to the developer transporting rotary body, and the surface of the magnetic developer adhered and transported on the developer transporting rotary body and the surface of the drum-shaped recording body opposite thereto are It is configured to use a developing device installed so that the gap is 0.05 to 0.5 mm. As described above, in the non-contact developing method, the developer (magnetic brush) does not contact the image portion of the electrostatic latent image carrier, so that the toner image already developed on the electrostatic latent image carrier is disturbed or scraped off. Since it is possible to prevent a decrease in image density, mixing of a developer, and color mixture, there is a feature that it is suitable for overlapping development.

However, the non-contact developing method as described above has a peculiar problem that the developability is low, and it is necessary to increase the developing electric field in order to obtain a sufficient developing density. In order to obtain a sufficient developing density in the non-contact developing method as described above, for example, the gap between the drum-shaped recording body and the surface of the magnetic developer on the developer transporting rotary member is set to a minimum (0.05
mm), the spike height of the magnetic brush is 50
It is difficult to make uniform alignment with variations of less than μm,
On the other hand, when the strength of the AC bias electric field is increased, the force of the electric field for developing the carrier on the background portion on the drum-shaped recording medium is increased. Therefore, in any of the above cases, the toner image of the first color is There is a problem that the first-color toner is mixed into the second-color developing device, such as scraping off the toner and decreasing the density.

Therefore, conventionally, there has been proposed a color image recording technique employing a new non-contact developing method for solving the above-mentioned problems in the non-contact developing method (JP-A-5-341615). And JP-A-5-347
No. 36).

That is, in the color image recording method disclosed in Japanese Unexamined Patent Publication No. 5-341615, the latent image forming step and the developing step are repeated a plurality of times on the electrostatic latent image carrier to form toner images of a plurality of colors. After that, in a color image forming apparatus that forms a color image by transferring the toner image to a recording sheet at a time, at least the developing bias voltage in the developing process after the second process is an AC voltage with a DC voltage superimposed, and For the AC voltage, the time for changing the voltage for developing the toner on the electrostatic development carrier from the maximum voltage to the minimum voltage is set to a voltage that is more than half of one cycle of the AC component. As a result, the moving acceleration of the toner that develops the electrostatic latent image on the electrostatic latent image carrier toward the electrostatic latent image carrier changes from the maximum to the minimum. Time was long that, thereby improving the developing property.

Further, the developing device disclosed in Japanese Unexamined Patent Publication No. 5-34736 opposes the photoconductor in the developing device which carries the developer onto the developing sleeve and causes the toner to fly in the oscillating electric field to perform the developing. A plate-like member having an electrode is provided in the upstream portion of the developing unit so as to be in contact with the developing sleeve to form a first oscillating electric field between the electrode and the developing sleeve, and a second vibrating member between the photosensitive member and the developing sleeve. An electric field is formed, and the first oscillating electric field is set to be stronger than the second oscillating electric field, whereby the toner particles are separated from the carrier and fly to separate the toner cloud from the toner cloud. It is generated to improve the developability.

[0010]

However, the color image forming apparatus adopting the new non-contact developing method has the following problems. That is, JP-A-5
In the color image forming apparatus disclosed in Japanese Patent Publication No.-341615, the time required for the acceleration in the direction of moving the toner onto the electrostatic latent image carrier to change from the maximum to the minimum can be lengthened. Since the time for the maximum acceleration is short, the development density remains at an insufficient level. Therefore, in order to obtain a sufficient development density, it is necessary to further increase the development electric field. However, if the amplitude of the alternating voltage of the development bias voltage is increased to increase the development electric field, the already-developed There is a problem that the density of the toner image on the latent image carrier is lowered, the color is mixed, and the toner is mixed from the toner image.

On the other hand, the developing device disclosed in Japanese Unexamined Patent Publication No. 5-34736 is a member that abuts on the developing sleeve in the developing area in order to effectively generate the toner cloud by the first oscillating electric field as described above. It is not possible to form a sufficient amount of the developer layer in the developing area because it is necessary to dispose the (electrode), and therefore it is necessary to set the first oscillating electric field strength to a high level, and the toner fogging on the background portion occurs. There is a problem that it occurs.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and its object is to provide a toner image already developed on the electrostatic latent image carrier. Even if there is a decrease in density of the toner image or color mixture,
Another object of the present invention is to provide an image forming apparatus capable of reliably preventing toner from mixing in the toner image and capable of always forming an image having a sufficient image density.

[0013]

SUMMARY OF THE INVENTION An image forming apparatus of the present invention is a developer carrier which is disposed so as to face the electrostatic latent image carrier and carries a two-component developer composed of toner and a magnetic carrier. And a developing bias power source for applying a developing bias voltage between the electrostatic latent image bearing member and the developer bearing member. For the electrostatic latent image carrier on which an electrostatic latent image is formed according to the information and the developing bias power source, a DC voltage is applied as the developing bias voltage by superimposing two kinds of alternating voltages having different frequencies and different amplitudes. It is characterized in that it is configured to.

Further, in the above-mentioned technical means, the image forming apparatus of the present invention has two types of alternating voltage having different frequencies and different amplitudes, and one of the alternating voltage on the low frequency side is
The cycle is set to be an integral multiple of one cycle of the high frequency side AC voltage, or the amplitude of the low frequency side AC voltage is set to be smaller than the amplitude of the high frequency side AC voltage. It is also a thing.

In the above technical means, the developing bias power source can apply a DC voltage as the developing bias voltage, which is a superposition of two kinds of AC voltages having different frequencies and amplitudes, and further, the cycle and the amplitude of the AC component. Any configuration may be used as long as the configuration can be changed.

In the above technical means, basically, two types of AC components of the developing bias voltage, that is, an AC voltage on the high frequency side and an AC voltage on the low frequency side, are used. Each of them is used. The frequency and amplitude of the alternating voltage in the frequency range are preferably set in the following ranges.

The AC voltage on the high frequency side has a frequency in the range of 2 to 10 kHz and an amplitude of 0.5 to 1 kV.
It is set to each range. When the frequency is less than 2 kHz, the developing property is improved, but density unevenness and carrier adhesion corresponding to the frequency occur in the developed toner image. On the contrary, when the frequency exceeds 10 kHz, the toner is liable to vibrate in the developing electric field due to the developing bias voltage. Cannot be followed, the developability tends to deteriorate, and a high-quality image cannot be obtained. On the other hand, when the amplitude is less than 0.5 kV, the developing electric field for developing the toner becomes small, so the developability does not improve, and conversely, 1 k
When it exceeds V, the developing electric field for developing the toner becomes large, so that the developability is improved, but toner fogging to the background portion is likely to occur, and moreover, carrier adhesion to the background portion due to the developing electric field and toner already developed As the image is pulled back, density decrease and color mixing occur.

Regarding the alternating voltage on the low frequency side,
Its frequency is 0.1 to 5 kHz, preferably 1 to 2 kHz
In the range of z, the amplitude is set in the range of 0.01 to 0.5 kV. When the frequency is less than 0.1 kHz, the developing property is improved, but density unevenness and carrier adhesion corresponding to the frequency occur in the developed toner image. On the contrary, when it exceeds 5 kHz,
Since the carrier cannot follow the vibration of the developing electric field and the adhesive force between the toner and the carrier cannot be reduced, the developability tends to deteriorate, and a high-quality image tends not to be obtained. Further, if the amplitude is less than 0.01 kV, an electric field sufficient to vibrate the carrier cannot be formed, so that the developability does not improve. If the amplitude exceeds 0.5 kV, carrier adhesion to the background portion due to the developing electric field, The already developed toner image is pulled back to cause a decrease in density and color mixture.

The image forming apparatus of the present invention is particularly effective in a color image forming apparatus, but may be a monochromatic image forming apparatus. In the case of a color image forming apparatus, 2 colors, 3
It may be an apparatus for forming a color image of four colors or four colors, and the developing bias voltage as described above may be applied in at least the second and subsequent developing steps, but the first developing You may comprise so that it may be applied in a process. Further, the electrostatic latent image carrier is not limited to the photoconductor in the electrophotographic recording system, but may be a dielectric in the electrostatic recording system. Note that the present invention is particularly effective in the case of an image forming apparatus that employs an overlapping development method that uses a non-contact developing method that uses a two-component developer. It is also possible to apply to an image forming apparatus adopting the contact developing method.

[0020]

According to the image forming apparatus of claim 1, the carrier having a larger mass than the toner is vibrated by the alternating electric field on the low frequency side of the developing bias voltage, so that the toner can be easily separated from the carrier. It is possible to obtain a sufficient image density. In the conventional non-contact developing method, unlike the contact developing method, the adhesive force between the toner and the carrier is not canceled by the adhesive force between the toner and the electrostatic latent image carrier, so the developability is considered to be low. To be In this respect, in the present invention, the influence of the adhesive force between the toner and the carrier is reduced by vibrating the carrier by the AC electric field on the low frequency side.

According to another aspect of the image forming apparatus of the present invention, for two types of AC voltage in the developing bias voltage, one cycle of the AC voltage on the low frequency side is an integral multiple of one cycle of the AC voltage on the high frequency side. By setting so that
Since no waviness due to two alternating electric fields having different frequencies is generated in the developing electric field, good development can be performed without uneven development due to the waviness.

According to the image forming apparatus of the third aspect, the amplitude of the alternating voltage on the low frequency side of the two kinds of alternating voltage in the developing bias voltage is smaller than the amplitude of the alternating voltage on the high frequency side. By setting, the carrier can be surely vibrated without causing the carrier to adhere to the toner image (image), and good development can be performed.

[0023]

The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a color image recording apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a photoconductor drum as an electrostatic latent image carrier, and around the photoconductor drum 1 along the rotation direction thereof, a first charger 2a and a first charger 2a as electrophotographic recording means. One latent image forming means 3
a, a first developing device 4a, a second charging device 2b, a second latent image forming means 3b, a second developing means 4b, a pre-transfer corotron 5, a transfer corotron 6, a peeling corotron 7, a cleaner 8 and an optical static eliminator 9 in order. It is arranged. Also, 10a, 10b
Is the developing roller 40 of each of the first and second developing means 4a and 4b.
A developing bias power source for applying a developing bias voltage to a and 40b, and 11 is a recording sheet.

The photoconductor drum 1 is formed by forming a thin photoconductor layer on the surface of a cylindrical member made of a conductive material.
In this embodiment, a photosensitive layer made of, for example, a negatively charged organic photosensitive body (OPC) is used, the outer diameter of the drum is 100 mm, and the surface moving linear velocity, that is, the process speed is 160 mm / s. It is set.

As the first and second latent image forming means 3a and 3b, any means can be used as long as it can expose the photosensitive drum 1 according to image information. For example, any one of a laser writing device, an LED array, an exposure device including a liquid crystal light valve including a uniform light source and a liquid crystal micro-shutter, etc. may be used according to the purpose. Further, these first and second latent image forming means 3a and 3b may be any of those which perform image part exposure or non-image part (background part) exposure, and any of them may be used, if necessary. Is appropriately selected.

As the first developing device 4a, there was used a developing device which carries out development by a usual contact developing method using a two-component developer composed of negatively charged red toner and a ferrite particle carrier having an average particle diameter of 100 μm. Further, a DC voltage of, for example, -450V is applied to the developing roll 40a of the developing device 4a from the developing bias power source 10a.

On the other hand, as the second developing device 4b, a developing device for performing non-contact development using a two-component developer composed of toner and magnetic carrier was used. This second developing device 4b
As shown in FIG. 2, the developing roll 40b is composed of a rotatable cylindrical non-magnetic sleeve 41 and a magnet roll 42 fixedly installed therein and having a plurality of magnetic poles. After the two-component developer supplied to the cartridge is regulated to a constant thickness by the layer thickness regulating member 43, the two-component developer is conveyed to the developing area facing the photosensitive drum 1 as the non-magnetic sleeve 41 rotates.

In this embodiment, the second developing device 4b uses a two-component developer composed of a negatively charged black toner and a carrier having an average particle diameter of 40 μm in which magnetic powder such as magnetite is dispersed in a synthetic resin. The distance between the non-magnetic sleeve 41 of the developing roll 40 and the photosensitive drum 1 is 5
The non-magnetic sleeve 41 conveyed to the developing area at
The thickness of the upper developer layer is set to 350 μm.

Further, the non-magnetic sleeve 4 of the second developing device 4b
1, the outer diameter is 25 mm and the surface roughness is Rz = 20 μ.
m cylindrical body is used. Further, as the magnet roll 42, for example, one formed by winding a sheet-like magnet after magnetizing a developer carrying magnetic pole and a peeling magnetic pole on a magnetic support having a shaft is used. The sheet magnet is
As illustrated in FIG. 2, the N-pole and the S-pole are alternately arranged so as to have a magnetic flux density of 200 Gauss at a distance of about 2.5 mm on a surface of the sleeve facing the photoconductor drum 1, for example. It is magnetized and is arranged on the magnetic support with a magnetic plate interposed therebetween. Also, the magnet roll 42
The magnetic poles are fixed so that the substantially intermediate positions of adjacent magnetic poles of different polarities are closest to and oppose the surface of the photosensitive drum 1. As the sheet magnet, for example, 70 wt% of strontium-ferrite powder is added to chloroprene rubber.
% Of the rubber magnet was used. The magnetic plate may be, for example, chloroprene rubber containing 70 wt% of strontium-ferrite powder in an unmagnetized thickness of 3 m.
m magnetic sheet can be used.

The developing bias power source 10b is a non-magnetic sleeve 41 in the developing roll 40b of the second developing device 4b.
In addition, a DC voltage in which two types of AC voltages having different frequencies and amplitudes are superimposed is applied. In this embodiment, the developing bias power source 10b includes a high frequency AC voltage generator 21 for generating a high frequency side AC voltage and a low frequency AC voltage generator for generating a low frequency side AC voltage as shown in FIG. 22
And a DC voltage generator 23 that generates a DC voltage,
High frequency AC voltage generator 21 and low frequency AC voltage generator 22
After the two AC voltages having different frequencies and different amplitudes generated from are superposed through the operational amplifiers 24 and 25, the superposed AC voltage is superposed on the DC voltage generated from the DC voltage generator 23 by the power amplifier 26, That is, as a developing bias voltage, the developing roll 4 of the second developing device 4b.
It is configured to be applied to 0b.

In this embodiment, as shown in FIG.
The frequency from the high frequency AC voltage generator 21 is, for example, 6 kHz.
A high frequency AC voltage having a rectangular signal waveform of z is generated (FIG. 4a), and one cycle of the low frequency AC component is 6 times as long as one cycle of the high frequency AC component from the low frequency AC voltage generator 22. A low-frequency AC voltage having a rectangular signal waveform with a frequency of, for example, 2 kHz is generated (FIG. 4b). Further, the amplitudes (voltages) of the high frequency AC voltage and the low frequency AC voltage are set to 800V and 50V, respectively. Further, the DC voltage generator 23 generates a DC voltage of -450 V in order to prevent toner fogging in the background portion and mixing of the second toner into the first toner image. Then, by superimposing the AC component after the two AC components are superposed on the DC component, a developing bias voltage having a signal waveform synthesized as shown in FIG. 4C is output.

Next, the operation of the apparatus of this embodiment will be described.

First, a first color (red) toner image is formed on the photosensitive drum 1. That is, the photosensitive drum 1 is rotationally driven in the arrow direction by a driving unit (not shown),
As shown in (a), the surface of the photosensitive layer of the drum 1 is set to a predetermined potential (for example, -600V) by the first charger 2a.
Is uniformly charged. Next, on the surface of the photosensitive drum 1, as shown in FIG. 5B, image exposure corresponding to the image of the first color is performed by the first latent image forming means 3a to form a first electrostatic latent image. To be done. Image exposure corresponding to the image of the first color is performed, for example, by image area exposure, and the photosensitive member surface potential of the drum 1 in the image area is, for example, −100 V.
Fall to. Thereafter, the electrostatic latent image corresponding to the first color image is developed by the first developing device 3a with the first color toner, that is, the red toner Ta, as shown in FIG. 5C. At that time, a DC voltage of, for example, −450 V is applied to the developing roller 40a of the first developing device 3a from the developing bias power source 10a.

Subsequently, a second-color (black) toner image is formed on the photosensitive drum 1 on which the first-color toner image is formed. That is, the surface of the photosensitive layer of the photosensitive drum 1 is as shown in FIG.
As shown in (d), the second charger 2b uniformly charges the film to a predetermined potential (for example, -650V), and at this time, the image portion potential of the first color rises to -600V. Then, on the surface of the photosensitive drum 1, as shown in FIG. 5E, the first latent image forming means 3b performs image exposure corresponding to the image of the second color to form a second electrostatic latent image. To be done. Image exposure corresponding to the second color is also performed by, for example, image part exposure,
The photoconductor surface potential of the photoconductor drum 1 in the image portion is lowered to, for example, −100V. Thereafter, the electrostatic latent image corresponding to the second color is developed with the second color toner, that is, the black toner Tb by the second developing device 3b as shown in the fifth (f).

The non-contact development by the second developing device 3b is
In the developing area, the black toner is secondly generated by the developing electric field formed by the developing bias voltage (FIG. 4c) which is a direct current voltage obtained by superimposing two kinds of alternating current voltages having different frequencies and amplitudes applied from the developing bias power source 10b. It is performed by flying and adhering to the electrostatic latent image.

Then, the two-color toner images of red and black thus formed on the photosensitive drum 1 are then subjected to pre-transfer charging by the pre-transfer corotron 5 if necessary, and their charge amounts are changed. After being increased to improve the transferability, the recording sheet 1 is charged by charging the transfer corotron 6.
1 is transferred. The recording sheet 11 after the transfer is peeled from the surface of the photoconductor drum 1 by the charging of the peeling corotron 7, and then is conveyed to a fixing device (not shown) to fix the toner images of the two colors, and is discharged to the outside of the apparatus. It As a result, a two-color image is formed.

On the other hand, the surface of the photoconductor drum 1 which has undergone the toner image transfer process and the recording sheet peeling process is cleaned by a cleaner 8 to remove residual toner and the like, and then exposed by an optical neutralizer 9 to remain. The electric charges are removed, and the device is ready for the next color image forming step.

The two-color image formed by the above steps has sufficient densities in both the first toner image (red) and the second toner image (black), and is attached to the carrier or to the background portion. The toner fogging did not occur, and there was no problem in practical use.

In the above embodiment, as the developing bias power source 10b for the second developing device, two types of alternating voltage having different frequencies and different amplitudes are used for the different alternating voltage generators 21, respectively.
However, the present invention is not limited to this. For example, the number of AC voltage generators is one, and the AC voltage from the generator is two types of AC voltage having different frequencies and amplitudes. It may be configured to distribute the voltage.

Further, although the rectangular wave is used as the waveform of the AC voltage of the second developing bias voltage in the above-mentioned embodiment, a triangular wave, a sine wave, or other waveform AC voltage may be used in the present invention. Also, the same effect can be obtained.

In the above embodiment, the case of a two-color color image forming apparatus has been described, but in the case of a three or more color image forming apparatus, each developing device (developer carrying member) of the second and subsequent colors. In all, the developing bias voltage composed of a DC voltage in which two kinds of AC voltages having different frequencies and amplitudes are superimposed may be applied. It should be noted that two types of AC voltages having different frequencies and amplitudes are superimposed on the first color developing device (which may use either the contact developing method or the non-contact developing method) in the color image forming apparatus. A developing bias voltage composed of the above DC voltage may be applied.

Further, instead of the magnetic pole arrangement of the magnet roll 42 in the second developing device 3b of the above-described embodiment (FIG. 2), in the present invention, the substantially middle position of the adjacent magnetic poles of the same polarity comes closest to the photosensitive drum. The magnetic poles may be arranged as described above. The present invention can also be applied to a developing system in which magnetic poles are arranged so that the magnetic poles of the magnet roll 42 are opposed to the photosensitive drum.

Furthermore, in the above-mentioned embodiment, the photoconductor is used as the latent image carrier, but a dielectric may be used in the present invention, and in this case, the dielectric is used in, for example, an electrostatic printer. Discharge head and JP-A-59-19085
It can be configured to form an electrostatic latent image by the ion flow control head disclosed in Japanese Patent Laid-Open No. 4 or the like.

[0045]

As described above, according to the present invention,
Since a DC voltage in which two kinds of AC voltages having different frequencies and amplitudes are superimposed is applied as a developing bias voltage, even if a toner image already developed is present on the electrostatic latent image carrier, the toner image is developed. It is possible to always form an image having a sufficient density without causing a decrease in density, color mixture, toner mixing from the toner image, or the like.

Further, since one cycle of the alternating voltage on the low frequency side in the developing bias voltage is set to an integral multiple of one cycle of the alternating voltage on the high frequency side, density unevenness due to undulation due to two kinds of alternating electric fields is generated. An image of excellent quality can be obtained without any occurrence.

Furthermore, since the amplitude of the alternating voltage on the low frequency side in the developing bias voltage is made smaller than the amplitude of the alternating voltage on the high frequency side, the carrier does not adhere to the previous toner image, and the carrier is not attached. Since it can be vibrated, an image having sufficient density can be obtained without deterioration of image quality due to carrier adhesion.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a configuration of a main part of a second developing device.

FIG. 3 is a block diagram showing a configuration of a developing bias power source of a second developing device.

4A and 4B show signal waveforms of respective voltage components generated by a developing bias power source of a second developing device, FIG. 4A is a signal waveform diagram of an AC component on a high frequency side, and FIG. 4B is a low frequency side. FIG. 3C is a waveform diagram of the AC bias component, and FIG. 3C is a waveform diagram of the developing bias voltage in which two types of AC components are superimposed on the DC voltage.

5A and 5B are explanatory diagrams showing the surface potential state of the photoconductor in each step when forming the toner images of the first and second colors by the apparatus of FIG.

[Explanation of symbols]

1 ... Photosensitive drum, 4b ... Second developing device, 10 ... Power source for developing bias, 40 ... Developing roll.

Front page continued (72) Inventor Shinji Sasahara, 2274 Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor, Heiwa Koren, 2274, Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A two-component developing device comprising an electrostatic latent image carrier on which an electrostatic latent image is formed according to image information, and a toner and a magnetic carrier which are disposed so as to face the electrostatic latent image carrier. An image forming apparatus comprising: a developing unit having a developer carrying member carrying an agent; and a developing bias power source for applying a developing bias voltage between the electrostatic latent image carrying member and the developer carrying member. The image forming apparatus is characterized in that the developing bias power source is configured to apply, as a developing bias voltage, a DC voltage in which two types of AC voltages having different frequencies and amplitudes are superimposed. 2. The apparatus according to claim 1, wherein two types of alternating voltage having different frequencies and amplitudes are such that one cycle of the alternating voltage on the low frequency side is an integral multiple of one cycle of the alternating voltage on the high frequency side. An image forming apparatus characterized by being set so that 3. The apparatus according to claim 1, wherein the two types of alternating voltage having different frequencies and different amplitudes have a smaller amplitude of the alternating voltage on the low frequency side than an amplitude of the alternating voltage on the high frequency side. An image forming apparatus, wherein the image forming apparatus is set to